Flat nonaqueous secondary batteries, often referred to as coin cells or button cells, generally include an electrode complex with positive and negative electrodes stacked upon each other and separated by a separator, and nonaqueous electrolyte, both contained in a space formed by an exterior case and a seal case.
A known flat nonaqueous secondary battery of the above configuration includes positive and negative electrodes that each have a current collector with a positive or negative compound layer on one side or such layers on both sides, where a portion of each current collector has no positive or negative compound layer upon it and thus is exposed to be used as a current collector tab. In such a flat nonaqueous secondary battery, such a current collector tab may be used to establish electrical connection between the collector and an exterior case or a seal case, both of which each serve as an electrode and terminal, as well.
An electrode assembly is known in which a positive electrode with such a configuration, inserted into a separator bag, and a negative electrode are stacked upon each other (for example, JP2004-509443A or JP2008-91100A). This separator bag is formed by disposing an insulating polymer film such as a polyester resin film having an adhesive on its surface between two separators and allowing the film to adhere to the separators using this adhesive (for example, JP2004-509443A), or welding the two separators together (for example JP2008-91100A).